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<h1>Modeling With Structs</h1>
<h2 class="subtitle">Notes</h2>

<h3>Tasty Sugar</h3>
<p>
  OK, so in terms of collections we have lists, maps, tuples, and now <em>keyword lists</em>? Well, kinda. Keywords lists are actually just a tiny
  dose of syntactic sugar.
</p>
<p>
  For example, here's the keyword list we passed to the <tt>defstruct</tt> macro:
</p>
<div class="highlight"><pre><span class="p">[</span> <span class="ss">method</span><span class="p">:</span> <span class="s2">""</span><span class="p">,</span> <span class="ss">path</span><span class="p">:</span> <span class="s2">""</span><span class="p">,</span> <span class="ss">resp_body</span><span class="p">:</span> <span class="s2">""</span><span class="p">,</span> <span class="ss">status</span><span class="p">:</span> <span class="no">nil</span> <span class="p">]</span>
</pre></div>
<p>
  Internally, keyword lists are represented as a list of tuples containing two values: an atom (the key) and the associated value. Here's what that looks like for the keyword list above:
</p>
<div class="highlight"><pre><span class="p">[</span> <span class="p">{</span><span class="ss">:method</span><span class="p">,</span> <span class="s2">""</span><span class="p">},</span> <span class="p">{</span><span class="ss">:path</span><span class="p">,</span> <span class="s2">""</span><span class="p">},</span> <span class="p">{</span><span class="ss">:resp_body</span><span class="p">,</span> <span class="s2">""</span><span class="p">},</span> <span class="p">{</span><span class="ss">:status</span><span class="p">,</span> <span class="no">nil</span><span class="p">}</span> <span class="p">]</span>
</pre></div>
<p>
  So keyword lists aren't yet another collection, but rather a tasty mashup
  of lists and tuples. 
</p>
<p>
  Keyword lists are most commonly used as a simple list of options.
  In contrast, maps are the go-to data structure for storing key/value
  pairs. 
</p>

<h3>Updating Structs</h3>
<p>
  In the video we changed the pattern in the <tt>route</tt> function heads 
  to verify that the argument is a <tt>Conv</tt> struct. For example:
</p>
<div class="highlight"><pre><span class="kd">def</span> <span class="n">route</span><span class="p">(%</span><span class="nc">Conv</span><span class="p">{</span> <span class="ss">method</span><span class="p">:</span> <span class="s2">"GET"</span><span class="p">,</span> <span class="ss">path</span><span class="p">:</span> <span class="s2">"/wildthings"</span> <span class="p">}</span> <span class="p">=</span> <span class="n">conv</span><span class="p">)</span> <span class="k">do</span>
  <span class="p">%{</span> <span class="n">conv</span> <span class="p">|</span> <span class="ss">status</span><span class="p">:</span> <span class="mi">200</span><span class="p">,</span> <span class="ss">resp_body</span><span class="p">:</span> <span class="s2">"Bears, Lions, Tigers"</span> <span class="p">}</span>          
<span class="k">end</span>
</pre></div>
<p>
  We didn't need to change the expression in the function body because the syntax for updating a struct is just like updating a map.
</p>
<p>
  However, we could have changed the update syntax to stipulate a <tt>Conv</tt> struct, like so:
</p>
<div class="highlight"><pre><span class="p">%</span><span class="nc">Conv</span><span class="p">{</span> <span class="n">conv</span> <span class="p">|</span> <span class="ss">status</span><span class="p">:</span> <span class="mi">200</span><span class="p">,</span> <span class="ss">resp_body</span><span class="p">:</span> <span class="s2">"Bears, Lions, Tigers"</span> <span class="p">}</span>
</pre></div>
<p>
  The difference is this verifies that the value being updated (<tt>conv</tt>) is indeed a struct of the type <tt>Conv</tt>, not a generic map. In this particular case the extra check doesn't gain us anything since the pattern in the function head requires the argument to be a <tt>Conv</tt> type. But sometimes it's worth adding that extra type safety check.
</p>
<p>
  To see what happens if we try to update a plain map, try this in an 
  <tt>iex</tt> session:
</p>
<div class="highlight"><pre><span class="n">iex</span><span class="o">&gt;</span> <span class="n">map</span> <span class="p">=</span> <span class="p">%{</span><span class="ss">method</span><span class="p">:</span> <span class="s2">"GET"</span><span class="p">,</span> <span class="ss">path</span><span class="p">:</span> <span class="s2">"/wildthings"</span><span class="p">}</span>

<span class="o">&gt;</span> <span class="p">%</span><span class="nc">Servy.Conv</span><span class="p">{</span> <span class="n">map</span> <span class="p">|</span> <span class="ss">status</span><span class="p">:</span> <span class="mi">200</span><span class="p">,</span> <span class="ss">resp_body</span><span class="p">:</span> <span class="s2">"Bears, Lions, Tigers"</span> <span class="p">}</span>
<span class="o">**</span> <span class="p">(</span><span class="nc">BadStructError</span><span class="p">)</span> <span class="n">expected</span> <span class="n">a</span> <span class="n">struct</span> <span class="n">named</span> <span class="nc">Servy.Conv</span><span class="p">,</span> <span class="ss">got</span><span class="p">:</span> <span class="p">%{</span><span class="ss">method</span><span class="p">:</span> <span class="s2">"GET"</span><span class="p">,</span> <span class="ss">path</span><span class="p">:</span> <span class="s2">"/wildthings"</span><span class="p">}</span>
</pre></div>
<p>
  This is yet another <em>compile-time</em> check that comes with using
  a struct as compared to a map.
</p>

<h3>Code So Far</h3>
<p>
  The code for this video is in the
<code>structs</code> directory found within the
  <tt>video-code</tt> directory of the <a href="https://s3.amazonaws.com/pragmaticstudio/courses/elixir/pragstudio-elixir-code.zip">code bundle</a>.
</p>



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        <a href="https://online.pragmaticstudio.com/courses/elixir/modules/1">1. Introduction</a>
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            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/1">Video</a><span class="time">1:56</span></li>
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            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/3">Video</a><span class="time">8:21</span></li>
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        <a href="https://online.pragmaticstudio.com/courses/elixir/modules/3">3. High-Level Transformations</a>
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        <a href="https://online.pragmaticstudio.com/courses/elixir/modules/4">4. Parse Request Line</a>
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            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/7">Video</a><span class="time">10:21</span></li>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/8">Notes</a></li>
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        <a href="https://online.pragmaticstudio.com/courses/elixir/modules/5">5. Route and Response</a>
        <ul>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/9">Video</a><span class="time">6:40</span></li>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/10">Notes</a></li>
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        <a href="https://online.pragmaticstudio.com/courses/elixir/modules/6">6. Function Clauses</a>
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            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/11">Video</a><span class="time">6:28</span></li>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/12">Notes</a></li>
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        <a href="https://online.pragmaticstudio.com/courses/elixir/modules/7">7. Request Params and Status Codes</a>
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            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/13">Video</a><span class="time">8:45</span></li>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/14">Notes</a></li>
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        <a href="https://online.pragmaticstudio.com/courses/elixir/modules/8">8. Rewrite Paths and Track 404s</a>
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            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/15">Video</a><span class="time">9:31</span></li>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/16">Notes</a></li>
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        <a href="https://online.pragmaticstudio.com/courses/elixir/modules/9">9. Serve Static Files</a>
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            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/17">Video</a><span class="time">11:27</span></li>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/18">Notes</a></li>
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        <a href="https://online.pragmaticstudio.com/courses/elixir/modules/10">10. Module Attributes</a>
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            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/19">Video</a><span class="time">3:00</span></li>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/20">Notes</a></li>
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        <a href="https://online.pragmaticstudio.com/courses/elixir/modules/11">11. Organizing Code</a>
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            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/21">Video</a><span class="time">6:30</span></li>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/22">Notes</a></li>
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        <a href="https://online.pragmaticstudio.com/courses/elixir/modules/12">12. Modeling With Structs</a>
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            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/23">Video</a><span class="time">11:09</span></li>
            <li class="here"><a href="https://online.pragmaticstudio.com/courses/elixir/steps/24">Notes</a></li>
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        <a href="https://online.pragmaticstudio.com/courses/elixir/modules/13">13. Handle POST Requests</a>
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            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/25">Video</a><span class="time">10:32</span></li>
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        <a href="https://online.pragmaticstudio.com/courses/elixir/modules/14">14. Recursion</a>
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            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/27">Video</a><span class="time">13:17</span></li>
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        <a href="https://online.pragmaticstudio.com/courses/elixir/modules/15">15. Slicing and Dicing with Enum</a>
        <ul>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/29">Video: Part 1</a><span class="time">10:25</span></li>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/30">Video: Part 2</a><span class="time">11:51</span></li>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/31">Notes</a></li>
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        <a href="https://online.pragmaticstudio.com/courses/elixir/modules/16">16. Comprehensions</a>
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            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/32">Video</a><span class="time">11:15</span></li>
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        <a href="https://online.pragmaticstudio.com/courses/elixir/modules/18">18. Test Automation</a>
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            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/36">Video</a><span class="time">15:21</span></li>
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        <a href="https://online.pragmaticstudio.com/courses/elixir/modules/19">19. Rendering JSON</a>
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            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/38">Video</a><span class="time">06:47</span></li>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/39">Notes</a></li>
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        <a href="https://online.pragmaticstudio.com/courses/elixir/modules/20">20. Web Server Sockets</a>
        <ul>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/40">Video</a><span class="time">19:11</span></li>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/41">Notes</a></li>
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      <li class="">
        <a href="https://online.pragmaticstudio.com/courses/elixir/modules/21">21. Concurrent, Isolated Processes</a>
        <ul>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/42">Video: Part 1</a><span class="time">12:07</span></li>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/43">Video: Part 2</a><span class="time">10:21</span></li>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/44">Notes</a></li>
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        <a href="https://online.pragmaticstudio.com/courses/elixir/modules/22">22. Sending and Receiving Messages</a>
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            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/45">Video</a><span class="time">19:38</span></li>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/46">Notes</a></li>
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        <a href="https://online.pragmaticstudio.com/courses/elixir/modules/23">23. Asynchronous Tasks</a>
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            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/47">Video</a><span class="time">20:19</span></li>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/48">Notes</a></li>
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        <a href="https://online.pragmaticstudio.com/courses/elixir/modules/24">24. Stateful Server Processes</a>
        <ul>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/49">Video: Part 1</a><span class="time">8:09</span></li>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/50">Video: Part 2</a><span class="time">11:55</span></li>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/51">Video: Part 3</a><span class="time">9:49</span></li>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/52">Video: Part 4</a><span class="time">8:59</span></li>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/53">Notes</a></li>
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        <a href="https://online.pragmaticstudio.com/courses/elixir/modules/25">25. Refactoring Toward GenServer</a>
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            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/54">Video</a><span class="time">21:12</span></li>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/55">Notes</a></li>
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        <a href="https://online.pragmaticstudio.com/courses/elixir/modules/26">26. OTP GenServer</a>
        <ul>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/56">Video</a><span class="time">16:57</span></li>
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        <a href="https://online.pragmaticstudio.com/courses/elixir/modules/27">27. Another GenServer</a>
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            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/58">Video</a><span class="time">9:00</span></li>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/59">Notes</a></li>
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        <a href="https://online.pragmaticstudio.com/courses/elixir/modules/28">28. Linking Processes</a>
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            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/60">Video</a><span class="time">13:38</span></li>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/61">Notes</a></li>
        </ul>
      </li>
      <li class="">
        <a href="https://online.pragmaticstudio.com/courses/elixir/modules/29">29. Fault Recovery with OTP Supervisors</a>
        <ul>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/62">Video: Part 1</a><span class="time">13:39</span></li>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/63">Video: Part 2</a><span class="time">6:13</span></li>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/64">Notes</a></li>
        </ul>
      </li>
      <li class="">
        <a href="https://online.pragmaticstudio.com/courses/elixir/modules/30">30. Final OTP Application</a>
        <ul>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/65">Video</a><span class="time">15:22</span></li>
            <li class=""><a href="https://online.pragmaticstudio.com/courses/elixir/steps/66">Notes</a></li>
            <li class="not-completable"><a href="https://online.pragmaticstudio.com/courses/elixir/next_steps">Next Steps</a></li>
            <li class="not-completable"><a href="https://online.pragmaticstudio.com/courses/elixir/evaluation">Evaluation</a></li>
        </ul>
      </li>
  </ul>
</div>


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